This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. BipA is a GTPase induced in response to BPI (bacteriocidal/permeability-increasing protein), an antimicrobial polypeptide produced by granulocytes. It is a large protein (60 kDa) comprised of at least three distinct domains, a N-terminal GTPase, a central domain of unknown function and a C-terminal domain exhibiting weak sequence similarity to domain IV of EF-G. The role of BipA in bacterial resistance to host defense mechanism has not been defined although initial data suggest that it may function to regulate pedestal formation, flagella-mediated motility and resistance to BPI. The aim of this project is to determine the conformation of BipA in various nucleotide bound states and then subsequently, in complex with associating proteins. Crystallization screens of several BipA homologs in their unbound, GTP- and GDP-bound forms have been carried out. Crystals of full-length Salmonella typhimurium in the unbound and GMP-PNP bound state have been grown using hanging drop technique from both PEG and ammonium sulfate conditions. Crystals of the unbound form of BipA belong to space group P21 with unit cell dimensions a = 89.5 A, b = 84.1 A, c = 95.6 A, b = 106.2 and have diffraction limits of 1.7 and 2.4 A for the native and selenomethionine derivatives crystals, respectively. Additional optimization of the crystals is required. Structure determination will be done using MAD or SAD phasing techniques.